Abstract: A security system for protecting articles (8), the system comprising at least one Electronic Article Surveillance (EAS) loop (1) , one Emitting Unit (7) and one Detecting Unit (9) attached to each article (8) to be protected, the Detecting Unit (9) having a detector to detect electromagnetic fields emitted by the EAS loop (4) and the Emitting Unit (7) and to distinguish between them, and an alarm generator for generating an alarm if a predetermined sequence of fields is detected. The system combines existing EAS loops (4) normally present in a retail store with Emitting Units (7) and Detecting Units (9) so as to monitor movement of articles (8), especially supermarket trolleys, around the retail store.